A few habits make every extension more reliable. When you shoot, leave some room around the product so later crops to square or vertical are easy, and let the AI image extender handle the photos that were framed too tight.
If you need the product to stay at exactly its original pixel size, extend the canvas by hand in an editor instead. For very large changes, such as square to 21:9, try two smaller steps.
Keep the original next to the approved version in the same folder so you can compare or redo it later.
When several people on a team prepare listings, agree on the ratio, position and note for each channel, so every product in the catalog is processed the same way.
Review results at full size on a large screen before upload, because small changes at the edges are easy to miss on a phone.
Finally, remember that shoppers trust photos that match the item they receive, so treat the extended area as a backdrop and never as a promise about what is in the box.